Scanning device

ABSTRACT

A scanning device includes an MEMS mirror mechanism that swings a mirror with respect to a first axial line as a central line and swings the mirror with respect to a second axial line as a central line, and a control unit that generates a first drive signal for swinging the mirror with respect to the first axial line as a central line and a second drive signal for swinging the mirror with respect to the second axial line as a central line. In a lighting-on period in which a light source emits laser light in one swing of the mirror with respect to the second axial line as a central line, the control unit generates the first drive signal and the second drive signal by repeating a process of generating N pieces (N is an integer of two or greater) of second signal elements which respectively constitute the second drive signal with respect to a first signal element in a ½ cycle period in the first drive signal.

TECHNICAL FIELD

The present disclosure relates to a scanning device.

BACKGROUND ART

As a scanning device, for example, a scanning device that performs scanning with laser light by using a MEMS (micro electro mechanical systems) mirror mechanism to display an image is known. In the scanning device, for example, an image of one frame or two frames is formed by m times of reciprocation (m: an integer of two or greater) of an irradiation region of laser light in a horizontal direction, and one time of reciprocation of the irradiation region of the laser light in a vertical direction. Patent Literature 1 (Japanese Unexamined Patent Publication No. 2006-276634) discloses a technology in which synchronization is performed at the time of initiating one frame and at the time of terminating one frame between a horizontal drive signal and a vertical drive signal for driving the MEMS mirror mechanism.

SUMMARY OF INVENTION

However, for example, in a case where a mirror is caused to be resonated by the horizontal drive signal, when a resonance frequency of the mirror varies in one frame due to a variation of an ambient temperature or the like, in the technology described in Patent Literature 1, it is difficult to correct a deviation that occurs in a corresponding relationship between the horizontal drive signal and the vertical drive signal until the one frame is terminated, and as a result, there is a concern that display of an image may be unstable.

An object of the present disclosure is to provide a scanning device capable of realizing stable scanning with laser light.

A scanning device according to an aspect of the present disclosure includes: a light source that emits laser light; an MEMS mirror mechanism that includes a mirror that reflects the laser light emitted from the light source, the MEMS mirror mechanism being configured to reciprocate an irradiation region of the laser light in a first direction by swinging the mirror with respect to a first axial line as a central line, and reciprocate the irradiation region in a second direction that intersects the first direction by swinging the mirror with respect to a second axial line as a central line that intersects the first axial line; and a control unit that generates a first drive signal for swinging the mirror with respect to the first axial line as a central line and a second drive signal for swinging the mirror with respect to the second axial line as a central line, and inputs the first drive signal and the second drive signal to the MEMS mirror mechanism. The first drive signal is an electric signal in which one swing of the mirror with respect to the first axial line as a central line is set as one cycle. The second drive signal is an electric signal in which one swing of the mirror with respect to the second axial line as a central line is set as one cycle. In a lighting-on period in which the light source emits the laser light in the one swing of the mirror with respect to the second axial line as a central line, the control unit generates the first drive signal and the second drive signal by repeating a process of generating N pieces (N is an integer of two or greater) of second signal elements which respectively constitute the second drive signal to correspond to a first signal element in a ½ cycle period in the first drive signal.

In the scanning device, the N pieces of second signal elements which respectively constitute the second drive signal are generated to correspond to the first signal element in a ½ cycle period in the first drive signal. In addition, generation of the second signal element is repeated in the lighting-on period in which the light source emits the laser light in the one swing of the mirror with respect to the second axial line as a central line. According to this, even when the MEMS mirror mechanism is influenced by a variation of an ambient temperature or the like, it is possible to suppress occurrence of a deviation in a corresponding relationship between the first drive signal and the second drive signal. Accordingly, according to the scanning device, stable scanning with laser light becomes possible. In addition, since the plurality of second signal elements are made to correspond to one piece of the first signal element, it is possible to finely control a waveform of the second drive signal in comparison to a case where one piece of the second signal element is made to correspond to one piece of the first signal element.

In the scanning device according to the aspect of the present disclosure, in the lighting-on period, the control unit may repeat a process of generating N pieces of the second signal elements that respectively have a period that is 1/N times a period of the first signal element to correspond to the first signal element. In this case, it is possible to easily generate the second signal element by a process using the frequency divider.

In the scanning device according to the aspect of the present disclosure, the first drive signal may be an electric signal for resonating the mirror with respect to the first axial line as a central line, the second drive signal may be an electric signal for linearly operating the mirror with respect to the second axial line as a central line, and the control unit may modulate a frequency of the first drive signal to conform to a resonance frequency of the mirror. According to this, even when the resonance frequency of the mirror varies due to a variation of an ambient temperature or the like, it is possible to more reliably suppress occurrence of a deviation in a corresponding relationship between the first drive signal and the second drive signal.

In the scanning device according to the aspect of the present disclosure, the control unit may generate the second drive signal by dividing a frequency of a feedback signal corresponding to a resonance frequency of the mirror in a frequency division ratio N1 (N1 is an integer of two or greater), and may generate the first drive signal by further dividing a frequency of the second drive signal in a frequency division ratio 2×N. Alternatively, the control unit may generate the second drive signal by dividing a frequency of a feedback signal corresponding to a resonance frequency of the mirror in a frequency division ratio N1 (N1 is an integer of two or greater), and may generate the first drive signal by dividing a frequency of the feedback signal in a frequency division ratio (2×N×N1).

In the scanning device according to the aspect of the present disclosure, the control unit may control the light source so that in the one swing of the mirror, an outgoing period corresponds to the lighting-on period and an incoming period corresponds to a lighting-off period. According to this, it is possible to suppress occurrence of a deviation in a corresponding relationship between the first drive signal and the second drive signal in the respective lighting-on periods. Note that, the lighting-off period is a period in which the control unit does not cause the light source to emit the laser light.

In the scanning device according to the aspect of the present disclosure, the control unit may control the light source so that in the one swing of the mirror, the outgoing period corresponds to a first lighting-on period and the incoming period corresponds to a second lighting-on period. According to this, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal and the second drive signal in the first lighting-on period and the second lighting-on period.

In the scanning device according to the aspect of the present disclosure, the control unit may generate the second signal element to correspond to the first signal element in a current one cycle period in the first drive signal. Alternatively, the control unit may generate the second signal element to correspond to the first signal element in an immediately previous one cycle period in the first drive signal. According to this, time delay when generating the second signal element can be minimized.

In the scanning device according to the aspect of the present disclosure, the MEMS mirror mechanism may include a first movable unit provided with the mirror, a second movable unit that supports the first movable unit to be swingable with respect to the first axial line as a central line, a support unit that supports the second movable unit to be swingable with respect to the second axial line as a central line, a drive coil that is provided in the second movable unit, and a magnet that generates a magnetic field acting on the drive coil. The electromagnetic drive type MEMS mirror mechanism is susceptible to a variation of an ambient temperature or the like, and thus repetition of generation of the second signal element as described above is particularly effective.

In the scanning device according to the aspect of the present disclosure, the light source may emit the laser light for projection display, and in a case where m times (m is an integer of two or greater) of reciprocation of an irradiation region in a first direction and one time of reciprocation of the irradiation region in a second direction correspond to each other, the control unit may generate the first drive signal and the second drive signal so that an image of one frame or two frames is formed by the m times of reciprocation of the irradiation region in the first direction and the one time of reciprocation of the irradiation region in the second direction. As described above, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal and the second drive signal, and thus, in this case, stable image display is possible.

In the scanning device according to the aspect of the present disclosure, the control unit may control the light source so that the laser light is modulated in correspondence with a position of the irradiation region. According to this, image display with higher quality is possible.

In the scanning device according to the aspect of the present disclosure, the control unit may repeat generation of the second signal element while fluctuating a frame rate. According to this, it is possible to easily and reliably repeat generation of the second signal element.

According to the present disclosure, it is possible to provide a scanning device capable of realizing stable scanning with laser light.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a scanning display system provided with a scanning device according to a first embodiment.

FIG. 2 is a configuration diagram of a MEMS mirror mechanism and a control unit of the scanning device illustrated in FIG. 1.

FIG. 3 is a view illustrating a scanning trajectory of laser light on a primary image plane of the scanning device illustrated in FIG. 1.

FIG. 4 is a view illustrating a relationship between a first drive signal and a second drive signal in the scanning device illustrated in FIG. 1.

FIG. 5 is a timing chart of the first drive signal and the second drive signal which are generated in the scanning device illustrated in FIG. 1.

FIG. 6 is an enlarged view illustrating a relationship between the first drive signal and the second drive signal in the scanning device illustrated in FIG. 1.

FIG. 7 is a view illustrating a relationship between the first drive signal and the second drive signal in the scanning device illustrated in FIG. 1.

FIG. 8 is a schematic view illustrating a variation of a drive signal and a scanning trajectory of laser light in the scanning device of the comparative example.

FIG. 9 is a schematic view illustrating a variation of a drive signal and a scanning trajectory of laser light in a scanning device (in a case where N is 2) of an example.

FIG. 10 is a configuration diagram of a modification example of the MEMS mirror mechanism and the control unit.

FIG. 11 is a configuration diagram of a modification example of the MEMS mirror mechanism and the control unit.

FIG. 12 is a timing chart of a first drive signal and a second drive signal which are generated by the MEMS mirror mechanism and the control unit illustrated in FIG. 11.

FIG. 13 is an enlarged view illustrating a relationship between the first drive signal and the second drive signal according to the modification example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Note that, the same reference numeral will be given to the same or corresponding portion in respective drawings, and redundant description will be omitted.

[Configuration of Scanning Device]

As illustrated in FIG. 1, for example, a scanning display system 10 is a laser scanning projection display that is mounted on a vehicle, and displays (projects and displays) an image to a windshield 100 of the vehicle. The scanning display system 10 includes a scanning device 1 and an optical system 11. The optical system 11 includes a plurality of planar mirrors 11 a and 11 b, a concave mirror 11 c, and a windshield 100. The windshield 100 functions as an optical element on a rearmost stage in the optical system 11. Light L2 for projection display which is emitted from the scanning device 1 is sequentially reflected by the planar mirror 11 a, the planar mirror 11 b, the concave mirror 11 c, and the windshield 100, and is incident to an eye E of an observer.

The scanning device 1 includes a light source 2, a MEMS mirror mechanism 3, a light diffusion unit 4, and a control unit 5. The light source 2 emits laser light L1 for projection display. More specifically, the light source 2 includes a plurality of light emission units 2 a. For example, the plurality of light emission units 2 a are a red laser diode, a green laser diode, and a blue laser diode, respectively. The light emission units 2 a emits the laser light L1 having a wavelength in a visible region. The laser light L1 emitted from the light emission units 2 a is reflected by a plurality of mirrors 2 b including a dichroic mirror, proceeds on the same light path, and is incident to the MEMS mirror mechanism 3.

The MEMS mirror mechanism 3 includes a mirror 3 a that reflects the laser light L1 emitted from the light source 2. The MEMS mirror mechanism 3 is a drive mirror manufactured by a MEMS (micro electro mechanical systems) technology, and a drive type of the MEMS mirror mechanism 3 is an electromagnetic drive type (details thereof will be described later). The MEMS mirror mechanism 3 scans the light diffusion unit 4 with the laser light L1 by swinging the mirror 3 a with respect to a first axial line and a second axial line which are orthogonal to each other as a central line.

The light diffusion unit 4 diffuses the laser light L1 in the scanning by the MEMS mirror mechanism 3. For example, the light diffusion unit 4 is a transmission-type microlens array, and allows the laser light L1 in the scanning by the MEMS mirror mechanism 3 to be transmitted and diffuses the laser light L1. In the laser light L1 diffused by the light diffusion unit 4, light constituting an image is incident to the optical system 11 disposed on a rear stage of the light diffusion unit 4 as light L2 for projection display.

The control unit 5 controls the light source 2 and the MEMS mirror mechanism 3. As an example, when receiving an input signal indicating initiation of projection display, the control unit 5 initiates output of the light emission units 2 a of the light source 2. According to this, the laser light L1 is emitted from the light source 2. At substantially the same time, the control unit 5 initiates an operation of the MEMS mirror mechanism 3. According to this, in the MEMS mirror mechanism 3, swinging of the mirror 3 a is initiated, and the light diffusion unit 4 is scanned with the laser light L1 emitted from the light source 2. At this time, the control unit 5 changes a ratio of the laser light L1 emitted from each of the respective light emission units 2 a in correspondence with a scanning position of the laser light L1 (a position of an irradiation region with the laser light L1) in the light diffusion unit 4. According to this, light L2 for projection display (that is, light constituting an image in the laser light L1 diffused by the light diffusion unit 4) is sequentially reflected by the planar mirror 11 a, the planar mirror 11 b, the concave mirror 11 c, and the windshield 100, and is incident to the eye E of the observer.

[Configuration of MEMS Mirror Mechanism]

As illustrated in FIG. 2, the MEMS mirror mechanism 3 includes a first movable unit 31, a second movable unit 32, a support unit 33, a first drive coil 34, a second drive coil (drive coil) 35, and a magnet 37 in addition to the mirror 3 a. The mirror 3 a is provided in the first movable unit 31. The second movable unit 32 supports the first movable unit 31 to be swingable with respect to a first axial line A1 as a central line. The support unit 33 supports the second movable unit 32 to be swingable with respect to a second axial line A2 that intersects (here, that is orthogonal to) the first axial line A1 as a central line.

More specifically, the second movable unit 32 is formed in a frame shape to surround the first movable unit 31, and is connected to the first movable unit 31 through a pair of torsion bars 38 disposed on the first axial line A1. The support unit 33 is formed in a frame shape to surround the second movable unit 32, and is connected to the second movable unit 32 through a pair of torsion bars 39 disposed on the second axial line A2. The first movable unit 31, the second movable unit 32, the support unit 33, the pair of torsion bars 38, and the pair of torsion bars 39 are integrally formed, for example, by an SOI (silicon on insulator) substrate.

The first drive coil 34 is provided in the first movable unit 31. A first drive signal S1 for swinging the mirror 3 a with respect to the first axial line A1 as a central line is input to the first drive coil 34 from the control unit 5, and an electromotive force signal S3 is output to the control unit 5 from the first drive coil 34. The second drive coil 35 is provided in the second movable unit 32. A second drive signal S2 for swinging the mirror 3 a with respect to the second axial line A2 as a central line is input to the second drive coil 35 from the control unit 5. The magnet 37 generates a magnetic field acting on the first drive coil 34 and the second drive coil 35.

The first drive signal S1 is an electric signal that resonates the mirror 3 a with respect to the first axial line A1 as a central line. When the first drive signal S1 is input to the first drive coil 34, a Lorenz force acts on the first drive coil 34 due to a mutual operation with the magnetic field generated by the magnet 37. In addition to the Lorenz force, when using resonance of the mirror 3 a and the first movable unit 31 in a natural frequency, it is possible to resonate the mirror 3 a with respect to the first axial line A1 as a central line. Note that, the natural frequency is determined by a mass of the mirror 3 a and the first movable unit 31, a spring constant of the pair of torsion bars 38, and the like.

The second drive signal S2 is an electric signal for linearly operating the mirror 3 a with respect to the second axial line A2 as a central line. When the second drive signal S2 is input to the second drive coil 35, a Lorenz force acts on the second drive coil 35 due to a mutual operation with the magnetic field that is generated by the magnet 37. It is possible to linearly operate the mirror 3 a with respect to the second axial line A2 as a central line by using balance between the Lorenz force and an elastic force of the pair of torsion bars 39.

The electromotive force signal S3 is an electric signal for acquiring information relating to a vibration angle of the mirror 3 a or the like. When the first movable unit 31 is swung in the magnetic field generated by the magnet 37, an electromotive force is generated in the first drive coil 34 provided in the first movable unit 31. The electromotive force corresponds to the electromotive force signal S3.

[Relationship Between First and Second Drive Signals and Frame]

As illustrated in FIG. 2 and FIG. 3, the MEMS mirror mechanism 3 reciprocate an irradiation region of the laser light L in a horizontal direction (first direction) D1 by swinging the mirror 3 a with respect to the first axial line A1 as a central line, and reciprocate the irradiation region of the laser light L in a vertical direction (second direction that intersects the first direction) D2 by swinging the mirror 3 a with respect to the second axial line A2 as a central line. The control unit 5 generates the first drive signal S1 and the second drive signal S2 so that an image of one frame is formed by m times of reciprocation (m: an integer of two or greater) of the irradiation region of the laser light L1 in the horizontal direction D1 and one time of reciprocation of the irradiation region of the laser light L1 in the vertical direction D2.

Note that, FIG. 3 is a view illustrating a scanning trajectory of the laser light L1 on a primary image plane (here, a predetermined region in the light diffusion unit 4). In FIG. 3, a solid-line trajectory represents the scanning trajectory of the laser light L1 emitted from the light source 2. A broken-line trajectory represents a scanning trajectory of the laser light L1 in a case where the laser light L1 is not actually emitted from the light source 2, but the laser light L1 is assumed to be emitted. That is, in the scanning device 1, an image is formed by performing scanning with the laser light L1 so that a drawing period (lighting-on period: a period in which the control unit 5 causes the light source 2 to emit the laser light L1) and a returning period (lighting-off period: a period in which the control unit 5 does not cause the light source 2 to emit the laser light L1) are provided (details will be described later).

As illustrated in FIG. 4, the first drive signal S1 is a rectangular wave in which one swing of the mirror 3 a with respect to the first axial line A1 as a central line is set as one cycle T1. The second drive signal S2 is a triangular wave in which one swing of the mirror 3 a with respect to the second axial line A2 as a central line is set as one cycle T2. In the second drive signal S2, in the one swing of the mirror 3 a with respect to the second axial line A2 as a central line, an outgoing period T2 a in which the mirror 3 a rotates in one direction is longer than an incoming period T2 b in which the mirror 3 a rotates in a direction opposite to the one direction.

The outgoing period T2 a of the second drive signal S2 corresponds to a period obtained by accumulating the one cycle T1 of the first drive signal S1 n times (n: an integer of two or greater). The laser light L1 is emitted from the light source 2 during the outgoing period T2 a. That is, the outgoing period T2 a is a drawing period in which the laser light L1 is emitted from the light source 2. The incoming period T2 b of the second drive signal S2 corresponds to a period obtained by accumulating the one cycle T1 of the first drive signal S1 m-n times (m-n: an integer of one or greater and smaller than n (here, an integer of two or greater and smaller than n)). The laser light L is not emitted from the light source 2 during the incoming period T2 b. That is, the incoming period T2 b is a returning period for which the laser light L1 is not emitted from the light source 2. Note that, the scanning trajectory of the laser light L1 as illustrated in FIG. 3 is an example of a case where a relationship between the first drive signal S1 and the second drive signal S2 as illustrated in FIG. 4 is further simplified.

[Configuration of Control unit]

As illustrated in FIG. 2, the control unit 5 includes a PLL (phase locked loop) circuit 51. The PLL circuit 51 includes a phase comparator 51 a, a loop filter 51 b, and a VCO (voltage controlled oscillator) 51 c. The PLL circuit 51 generates a feedback signal S4 corresponding to a resonance frequency of the mirror 3 a, and outputs the feedback signal S4 to a frequency divider 52B to be described later.

Specifically, the electromotive force signal S3 superimposed on the first drive signal S1 is input to the phase comparator 51 a from the first drive coil 34. The phase comparator 51 a changes a voltage in correspondence with a variation of a phase of the electromotive force signal S3 that is input (that is, a variation of a phase corresponding to a resonance frequency of the mirror 3 a), and outputs a signal in which a voltage is changed. The loop filter 51 b removes a high-frequency component from the signal in which the voltage is changed by the phase comparator 51 a, and outputs the signal from which the high-frequency component is removed. The VCO 51 c changes a frequency in correspondence with a variation of a voltage in the signal from which the high-frequency component is removed by the loop filter 51 b, and outputs the signal in which the frequency is changed as the feedback signal S4.

The control unit 5 further includes frequency dividers 52A and 52B, a D/A converter 53, and constant current circuits 57 and 58. In this embodiment, the second drive signal S2 is generated by the frequency divider 52B and the D/A converter 53. In addition, the first drive signal S1 is generated by the frequency divider 52A.

The frequency divider 52B divides a frequency of the feedback signal S4 output from the VCO 51 c in a frequency division ratio N1 (N1 is an integer of two or greater) to generate the second drive signal S2 before D/A conversion. The second drive signal S2 before D/A conversion which is generated by the frequency divider 52B is input to the D/A converter 53 and the frequency divider 52A. The D/A converter 53 generates a second drive signal S2 after D/A conversion on the basis of the second drive signal S2 before D/A conversion. The D/A converter 53 inputs the generated second drive signal S2 to the second drive coil 35. At this time, the second drive signal S2 is converted into a current by the constant current circuit 58.

The frequency divider 52A further divides a frequency of the second drive signal S2 before D/A conversion which is generated by the frequency divider 52B in a predetermined frequency division ratio to generate the first drive signal S1. In this embodiment, the control unit 5 generates N (N is an integer of two or greater) pieces of second signal elements S2 ₁, which respectively constitute the second drive signal S2, to correspond to first signal elements S1 _(i) within a ½ cycle period in the first drive signal S1 (refer to FIG. 6). In this case, the frequency division ratio of the frequency divider 52A is set to “2×N”. The frequency divider 52A inputs the generated first drive signal S1 to the first drive coil 34. At this time, the first drive signal S1 is converted into a current by the constant current circuit 57.

FIG. 5 is a timing chart (illustrating a timing and a cycle at which a voltage value varies) of the first drive signal S1 and the second drive signal S2 which are generated by the frequency dividers 52A and 52B. FIG. 5 illustrates an example of a case where the frequency division ratio N1 of the frequency divider 52B is “4”, and the frequency division ratio of the frequency divider 52A is “4 (that is, “2×N” in a case where N is 2)“. That is, in the example in FIG. 5, the frequency divider 52B divides a frequency of” the feedback signal S4 into four frequencies, and thus the second drive signal S2 having a D/A conversion cycle t2 that is four times one cycle t1 in the feedback signal

S4 is obtained. Here, the D/A conversion cycle t2 corresponds to a period corresponding to one piece of second signal element to be described later. In addition, the frequency divider 52A further divides the frequency of the second drive signal S2 into four frequencies, and thus the first drive signal S1 in which a period t3 that is four times the D/A conversion cycle t2 is set as one cycle is obtained.

In the MEMS mirror mechanism 3, a resonance frequency of the mirror 3 a may vary due to a variation of an ambient temperature or the like. When the resonance frequency of the mirror 3 a varies, a phase of the electromotive force signal S3 varies. Accordingly, the control unit 5 can modulate the frequency of the first drive signal S1 and the second drive signal S2 to conform to the resonance frequency of the mirror 3 a by operating the PLL circuit 51 and the frequency dividers 52A and 52B as described above.

The control unit 5 further includes a memory 54, a timing signal generation unit 55, and an LD driver 56. The memory 54 stores image information for projection display. The timing signal generation unit 55 reads out image information corresponding to a scanning position of the laser light L1 on the basis of the signal (first drive signal S1) in which the frequency is divided by the frequency divider 52A from the memory 54, and transmits the read-out image information to the LD driver 56. The LD driver 56 controls the light source 2 so that the laser light L1 is modulated in correspondence with the scanning position of the laser light L1 (that is, so that a ratio of the laser light L1 emitted from each of the light emission units 2 a varies in correspondence with the scanning position of the laser light L1). Note that, the timing signal generation unit 55 may read out the image information corresponding to the scanning position of the laser light L1 from the memory 54 on the basis of the signal (second drive signal S2) of which a frequency is divided by the frequency divider 52B.

Generation of the first drive signal S1 and the second drive signal S2 by the control unit 5 will be described in more detail. Here, description will be given of a case where the frequency division ratio of the frequency divider 52A is “4” as illustrated in the example in FIG. 5. In this case, as illustrated in FIG. 6, the control unit 5 generates a second signal element S2 _(i) constituting the second drive signal S2 to correspond to a first signal element S1 _(i) in a current one cycle T1 in the first drive signal S1. More specifically, the control unit 5 generates two pieces of second signal elements S2 _(i) respectively constituting the second drive signal S2 to correspond to the first signal element S1 _(i), of ½ cycle in the current one cycle T1 in the first drive signal S1. Here, a period of one of the second signal elements S2 ₁ is a period (T¼) that is a half of a period (T½) of one piece of first signal element S1 _(i). That is, the period of the one first signal element S1 _(i) is equal to the sum of periods of two second signal elements S2 ₁. Here, the control unit 5 sets the period of the first signal element S1 _(i) to be a period conforming to the resonance frequency of the mirror 3 a on the basis of a variation of the phase of the electromotive force signal S3 with respect to the first signal element S1 _(i). In addition, the control unit 5 sets a period of the second signal element S2 ₁ so that the first signal element S1 _(i) and the second signal element S2 _(i) correspond to each other in a relationship of “1:N (here, two)” as described above, and sets a voltage value of the second signal element S2 _(i). Here, the one cycle T1 of the first drive signal S1 in FIG. 6 corresponds to the period t3 in FIG. 5. The period (T¼) of the second signal element S2 _(i) in FIG. 6 corresponds to the D/A conversion cycle t2 in FIG. 5.

The control unit 5 may generate the second signal element S2 _(i) constituting the second drive signal S2 to correspond to a first signal element S1 _(i-1) in an immediately previous one cycle T1 (one cycle T1 before the current one cycle T1 by one cycle) in the first drive signal S1. More specifically, the control unit 5 generates the first signal element S1 _(i) of ½ cycle in the current one cycle T1 in the first drive signal S1 corresponding to one cycle T1 on the basis of the first signal element S1 _(i-1) of ½ cycle in the immediately previous one cycle T1 (may be the first signal element S1 _(i-1) of the first-half ½ cycle in the immediately previous one cycle T1, or may be the first signal element S1 _(i-1) of the second-half ½ cycle in the immediately previous one cycle T1) in the first drive signal 51. Here, the control unit 5 sets the period of the first signal element S1 _(i) to be a period conforming to the resonance frequency of the mirror 3 a on the basis of a variation of a phase of the electromotive force signal S3 with respect to the first signal element S1 _(i-1). In addition, the control unit 5 generates the second signal element S2 _(i) constituting the second drive signal S2 in a number (2×N pieces (four pieces in the example in FIG. 6) of the second signal elements S2 ₁) corresponding to the one cycle T1 to correspond to the first signal element S1 _(i). Here, the control unit 5 sets a period of the second signal element S2 ₁ so that a period of two pieces of the second signal elements S2 _(i) becomes the same as a period of one piece of the first signal element S1 _(i), and sets a voltage value of the second signal element S2 ₁.

The control unit 5 repeats generation of the first signal element S1 _(i) and generation of the second signal element S2 _(i) as described above in both the drawing period and the returning period while controlling the light source 2 (refer to FIG. 4) so that the outgoing period T2 a corresponds to the drawing period and the incoming period T2 b corresponds to the returning period. According to this, in a case where the period of the first signal element S1 _(i) is constant as illustrated in the upper part of FIG. 7, and in a case where the period of the first signal element S1 _(i) varies in one frame due to a variation of the resonance frequency of the mirror 3 a as illustrated in the lower part of FIG. 7, a deviation does not occur in the corresponding relationship between the first drive signal S1 and the second drive signal S2. As described above, the control unit 5 repeats generation of the first signal element S1 _(i) and the second signal element S2 _(i) while fluctuating a frame rate (the number of frames processed per unit time).

However, the control unit 5 may repeat generation of the first signal element S1 _(i) and generation of the second signal element S2 _(i) at least in a lighting-on period from the viewpoint of performing stable scanning with the laser light L1. That is, in a case where the drawing period and the returning period are set as described above, the control unit 5 may repeat generation of the first signal element S1 _(i) and generation of the second signal element S2 ₁ at least in the outgoing period T2 a that is the drawing period (lighting-on period), and may not repeat generation of the first signal element S1 _(i) and generation of the second signal element S2 _(i) in the incoming period T2 b that is the returning period (lighting-off period).

Operation and Effect

In the scanning device 1, N pieces of the second signal elements S2 ₁ respectively constituting the second drive signal S2 are generated to correspond to the first signal element. S1 _(i) in a ½ cycle (half cycle) period in the first drive signal 51. In addition, generation of the second signal element S2 _(i) is repeated at least in the lighting-on period (the outgoing period T2 a in this embodiment) in which the light source 2 emits the laser light L1 in one swing of the mirror 3 a with respect to the second axial line A2 as a central line. According to this, even though the MEMS mirror mechanism 3 is influenced by a variation of an ambient temperature or the like, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2. Accordingly, according to the scanning device 1, stable scanning with the laser light L1, and further, stable image display (for example, image display in which occurrence of a flicker phenomenon is suppressed) become possible.

In the scanning device 1, the first drive signal S1 is an electric signal for resonating the mirror 3 a with respect to the first axial line A1 as a central line, the second drive signal S2 is an electric signal for linearly operating the mirror 3 a with respect to the second axial line A2 as a central line, and the control unit 5 modulates the frequency of the first drive signal S1 to conform to the resonance frequency of the mirror 3 a. According to this, even when the resonance frequency of the mirror 3 a varies due to a variation of an ambient temperature or the like, it is possible to more reliably suppress occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2. Particularly, in the control unit 5, since the PLL circuit 51 is used, it is not necessary to separately provide a configuration for measuring the resonance frequency of the mirror 3 a, and thus it is possible to realize reduction in size of the device and simplification of a configuration of the device.

In addition, in the scanning device 1, a plurality (N pieces) of the second signal elements S2 _(i) are made to correspond to one piece of the first signal element S1 _(i) (that is, the first signal element S1 _(i) and the second signal element S2 ₁ are made to correspond to each other in a relationship of “1:N”), it is possible to finely control a waveform of the second drive signal S2 in comparison to a case where one piece of the first signal element S1 _(i) and one piece of the second signal element S2 _(i) are made to correspond to each other (that is, the first signal element S1 ₁ and the second signal element S2 ₁ are made to correspond to each other in a relationship of “1:1”). Hereinafter, the effect will be described in more detail with reference to FIGS. 8 and 9.

FIG. 8 is a schematic view illustrating a relationship between a variation (a solid line) of a drive signal (the first drive signal S1 and the second drive signal S2) and a scanning trajectory (a broken line) of laser light L1 which corresponds to the variation of the drive signal in a scanning device of a comparative example. FIG. 9 is a schematic view illustrating a relationship between a variation (a solid line) of a drive signal (the first drive signal S1 and the second drive signal S2) and a scanning trajectory (a broken line) of the laser light L1 which corresponds to the variation of the drive signal in a scanning device of an example (a case where N is two). In FIGS. 8 and 9, a variation indicated by a solid line along a horizontal direction D1 corresponds to a variation of a voltage value of the first drive signal S1. In addition, a variation indicated by a solid line along a vertical direction D2 corresponds to a variation of a voltage value of the second drive signal S2.

As illustrated in FIG. 8, in the comparative example, the first drive signal S1 and the second drive signal S2 are generated so that the first signal element S1 _(i) and the second signal element S2 _(i) correspond to each other in a relationship of “1:1” in the lighting-on period. That is, a period (T½) of one piece of the first signal element S1 _(i) and a period of one piece of the second signal element S2 ₁ match each other. Accordingly, in the comparative example, the second drive signal S2 varies only twice in one cycle T1 in the first drive signal S1.

On the other hand, as illustrated in FIG. 9, in this example, in the lighting-on period, the first drive signal S1 and the second drive signal S2 are generated so that the first signal element S1 _(i) and the second signal element S2 _(i) correspond to each other in a relationship of “1:N (here, N is two)”. Accordingly, in this example, the second drive signal S2 varies four times (that is, “2×N” times) in one cycle T1 in the first drive signal S1.

As illustrated in FIGS. 8 and 9, swinging of the mirror 3 a which is desired to realize in the comparative example and the example (that is, ideal scanning trajectory of the laser light L1) is the same in each case. However, in the example, it is possible to finely vary the second drive signal S2 in comparison to the comparative example. Here, the second drive signal S2 has an arbitrary waveform that is generated when the D/A converter 53 varies an output voltage in a step shape. As in the example, when the first signal element S1 _(i) and the second signal element S2 ₁ are made to correspond to each other in a relationship of “1:N”, a step interval (that is, a period of one piece of the second signal element S2 ₁) for varying the output voltage can be shortened.

Specifically, the step interval in this example becomes 1/N times the step interval in the comparative example. According to this, it is possible to generate the waveform of the second drive signal S2 with more accuracy.

In addition, since the waveform of the second drive signal S2 can be generated with accuracy, the following effect is exhibited. In this embodiment, the mirror 3 a is operated to resonate in the horizontal direction D1 by the first drive signal S1, and the mirror 3 a is operated not to resonate in the vertical direction D2 by the second drive signal S2. In addition, as illustrated in FIG. 4, as the second drive signal S2, a saw-tooth wave is used. There is a concern that a frequency component close to the resonance frequency (hereinafter, referred to as “resonance frequency component”) of the mirror 3 a may be included in the second drive signal S2 that is the saw-tooth wave. In addition, in a case where the second drive signal S2 includes the resonance frequency component of the mirror 3 a, there is a concern that a phenomenon (so-called ringing) in which the mirror 3 a unintentionally resonates in the vertical direction D2 may occur. As a method of avoiding occurrence of the ringing, for example, it is considered that a vertical drive signal from which a high-frequency component derived by predetermined operation such as an FFT operation and a reverse FFT operation is removed (that is, an ideal signal waveform capable of driving the mirror 3 a in the vertical direction D2 without occurrence of the ringing) is reproduced by the D/A converter 53. However, typically, the ideal vertical drive signal has a complicated waveform including a portion that finely varies in a short time interval (a fine wave shape). Here, in this embodiment, since the first signal element S and the second signal element S2 ₁ are made to correspond to each other in a relationship of “1:N”, it is possible to more finely control the waveform of the second drive signal S2. As a result, it is possible to reproduce the second drive signal S2 for avoiding the above-described ringing with accuracy. That is, according to the scanning device 1 of this embodiment, it is possible to appropriately obtain an ideal signal waveform (a complicated waveform that finely varies) for avoiding the ringing.

In addition, in the scanning device 1, the control unit 5 repeats a process of generating N pieces of the second signal elements S2 _(i) that respectively have a period that is 1/N times the period of the first signal element S1 _(i) to correspond the first signal element S1 _(i) at least in the lighting-on period (the outgoing period T2 a that is a drawing period). In this case, it is possible to easily generate the second signal element S2 _(i) by a process using the frequency dividers 52A and 52B as described above.

As described above, in a case where the control unit 5 generates the second signal element S2 _(i) to correspond to the first signal element S1 _(i) or S in a ½ cycle period in the first drive signal S1, it is possible to make a process when generating the second signal element S2 _(i) easy. In addition, in a case where the control unit 5 generates the second signal element S2 _(i) to correspond to the first signal element S1 _(i) in a current one cycle T1 in the first drive signal S1, or in a case where the control unit 5 generates the second signal element S2 ₁ to correspond to the first signal element S1 _(i-1) in an immediately previous one cycle T1 in the first drive signal S1, time delay when generating the second signal element S2 _(i) can be minimized. In addition, in a case where the control unit 5 generates the second signal element S2 _(i) to correspond to the first signal element S1 _(i) in the current one cycle T1 in the first drive signal S1, even when the resonance frequency of the mirror 3 a varies in the middle of the first signal element S1 _(i) and the period of the first signal element S1 _(i) is shortened, it is possible to set the period of the second signal element S2 _(i) to a period corresponding to the period of the first signal element S1 _(i) by determining the period of the second signal element S2 _(i) with reference to the electromotive force signal S3 corresponding to the first signal element S1 _(i).

In the scanning device 1, the control unit 5 controls the light source 2 so that the outgoing period T2 a corresponds to the drawing period and the incoming period T2 b corresponds to the returning period, and repeats generation of the second signal element S2 _(i) at least in the drawing period that is the lighting-on period (in this embodiment, as an example, both the drawing period and the returning period). According to this, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2 in the lighting-on period. In addition, in a case where generation of the second signal element S2 ₁ is repeated even in the returning period that is the lighting-off period as in this embodiment, the following effect is exhibited. That is, in a case where the returning period is provided in the scanning with the laser light L1, since a temperature of the MEMS mirror mechanism 3 is lowered in the returning period in which the mirror 3 a is not irradiated with the laser light L1, the resonance frequency of the mirror 3 a is likely to fluctuate. Accordingly, in a case where the returning period is provided in the scanning with the laser light L1, repeating generation of the second signal element S2 _(i) as described above is particularly effective for suppressing occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2 in each drawing period. That is, since the first drive signal S1 and the second drive signal S2 correspond to each other even in the returning period, it is not necessary to adjust the deviation between the first drive signal S1 and the second drive signal S2 at the time of initiating the subsequent drawing period. In addition, when stopping the resonance operation of the mirror 3 a in the returning period, it is difficult to promptly swing the mirror 3 a at a high speed at the time of initiating the subsequent drawing period, and as a result, there is a concern that an image is blurred at the time of initiating the subsequent drawing period. In the scanning device 1, since the resonance operation of the mirror 3 a is not stopped by providing the first drive signal S1 corresponding to a plurality of cycles in the returning period, the resonance operation of the mirror 3 a becomes stable at the time of initiating the subsequent drawing period, and it is possible to effectively suppress an image from being blurred at the time of initiating the subsequent drawing period.

In the scanning device 1, the electromagnetic drive type MEMS mirror mechanism 3 is used. In the electromagnetic drive type MEMS mirror mechanism 3, the resonance frequency of the mirror 3 a is likely to vary due to a variation of a spring constant of the pair of torsion bars 38 due to a variation of an ambient temperature, a variation of a moment of inertia due to attachment of particles or the like, a variation of an attenuation coefficient of the pair of torsion bars 38 due to a variation of an atmospheric pressure, a variation of the spring constant of the pair of torsion bars 38 due to an operation of the second movable unit 32 with respect to the second axial line A2 as a central line, a variation of the spring constant and the attenuation coefficient of the pair of torsion bars 38 due to an aging variation of metal wires provided in the pair of torsion bars 38, or the like. The size of the MEMS mirror mechanism 3 is small, and thus fluctuation of the resonance frequency of the mirror 3 a is more significant in comparison to a large-sized mirror mechanism such as a galvano mirror. Accordingly, in a case where the electromagnetic drive type MEMS mirror mechanism 3 is used, repeating generation of the second signal element S2 _(i) as described above is particularly effective for suppressing occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2 in each drawing period.

In the scanning device 1, the control unit 5 controls the light source 2 so that the laser light L1 is modulated in correspondence with a scanning position of the laser light L1. According to this, image display with higher quality is possible. Note that, when an absorption rate of the laser light L1 in the mirror 3 a fluctuates due to modulation of the laser light L1, the resonance frequency of the mirror 3 a fluctuates. Accordingly, in this case, repeating generating of the second signal element S2 _(i) as described above is particularly effective for suppressing occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2 in each drawing period.

In the scanning device 1, the control unit 5 repeats generation of the second signal element S2 _(i) while fluctuating the frame rate. According to this, it is possible to easily and reliably repeat generation of the second signal element S2 _(i). This is a finding found independently from a finding in the related art in which the frame rate is typically fixed, and enables stable image display.

In the scanning device 1, the light source 2 emits the laser light L1 for projection display, and in a case where m times (m is an integer of two or greater) of reciprocation of the irradiation region in the horizontal direction D1 and one time of reciprocation of the irradiation region in the vertical direction D2 correspond to each other, the control unit 5 generates the first drive signal S1 and the second drive signal S2 so that an image of one frame or two frames is formed by the m times of reciprocation of the irradiation region in the horizontal direction D1 and the one time of reciprocation of the irradiation region in the vertical direction D2. As described above, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2. In this case, stable image display is possible.

In the scanning device 1, the control unit 5 generates the second drive signal S2 by dividing the frequency of the feedback signal S4 corresponding to the resonance frequency of the mirror 3 a in a frequency division ratio N1 (N1 is an integer of two or greater), and generates the first drive signal S1 by further dividing the frequency of the second drive signal S2 in a frequency division ratio 2×N. In this embodiment, first, the first stage of frequency divider 52B generates the second drive signal S2 from the feedback signal S4, and the second stage of frequency divider 52A generates the first drive signal S1 from the second drive signal S2. In this manner, when the frequency dividers 52A and 52B are serially connected, it is possible to simplify setting of the frequency division ratio of the frequency dividers 52A and 52B. For example, in a case where it is desired to change the integer N that defines the ratio between the first signal element S1 _(i) and the second signal element S2 _(i), only the frequency division ratio of the frequency divider 52A may be changed, and it is not necessary to change the frequency division ratio of the frequency divider 52B. That is, it is possible to define the ratio between the first signal element S1 _(i) and the second signal element S2 _(i) by only the frequency division ratio of the frequency divider 52A.

Modification Example

The present disclosure is not limited to the one embodiment. For example, the light source 2 is not limited to a light source that uses a laser diode (semiconductor laser), and may be a light source that uses a surface-emitting laser, an SLD (super luminescent diode), or the like. In addition, a drive type of the MEMS mirror mechanism 3 is not limited to the electromagnetic drive type, and may be an electrostatic drive type, a piezoelectric drive type, a thermal drive type, or the like. In addition, the light diffusion unit 4 is not limited to the transmission type microlens array, and may be reflection type microlens array, a micro mirror array, a diffraction lattice, a fiber optic plate, or the like.

In addition, as illustrated in FIG. 10, the MEMS mirror mechanism 3 may further include an electromotive force monitoring coil 36. The electromotive force monitoring coil 36 is provided in the first movable unit 31 to be located on an inner side of the first drive coil 34. The electromotive force signal S3 is output to the control unit 5 (more specifically, the phase comparator 51 a of the PLL circuit 51) from the electromotive force monitoring coil 36. When the first movable unit 31 is swung in the magnetic field generated by the magnet 37, an electromotive force is generated in the electromotive force monitoring coil 36 provided in the first movable unit 31. The electromotive force corresponds to the electromotive force signal S3. Even in this case, generation of any of the second signal element S2 is possible.

However, in the case of acquiring the electromotive force generated in the first drive coil 34 as the electromotive force signal S3, the following advantage is attained. That is, the first drive coil 34 is wound along an outer edge of the first movable unit 31 to swing the first movable unit 31 with high efficiency. In this case, a winding diameter of the first drive coil 34 increases, and thus a large electromotive force can be obtained even in a small number of turns. In addition, only a wire electrically connected to the first drive coil 34 passes through the torsion bars 38, and thus manufacturing of the MEMS mirror mechanism 3 can become easy.

In addition, as illustrated in FIG. 11, the scanning device 1 may include a control unit 5A instead of the control unit 5. The control unit 5A is different from the control unit 5 in the following configuration.

That is, the control unit 5A is configured to generate the second drive signal S2 by dividing the frequency of the feedback signal S4 in a frequency division ratio N1 (N1 is an integer of two or greater), and to generate the first drive signal S1 by dividing the frequency of the feedback signal S4 in a frequency division ratio (2×N×N1).

Specifically, in the control unit 5A, the feedback signal S4 output from the VCO 51 c is input to not only the frequency divider 52B but also the frequency divider 52A. On the other hand, in the control unit 5A, the second drive signal S2 before D/A conversion which is generated by the frequency divider 52B is not input to the frequency divider 52A. That is, in the control unit 5A, the frequency dividers 52A and 52B are configured to independently generate the first drive signal S1 and the second drive signal S2 from the feedback signal S4.

More specifically, as in the frequency divider 52B in the control unit 5, the frequency divider 52B in the control unit 5A generates the second drive signal S2 before D/A conversion by dividing the frequency of the feedback signal S4 in a frequency division ratio N1 (N1 is an integer of two or greater). On the other hand, the frequency divider 52A in the control unit 5A generates the first drive signal S1 by dividing the frequency of the feedback signal S4 in a frequency division ratio (2×N×N1) differently from the frequency divider 52A in the control unit 5.

FIG. 12 is a timing chart (illustrating a timing and a cycle at which a voltage value varies) of the first drive signal S1 and the second drive signal S2 which are generated by the frequency dividers 52A and 52B in the control unit 5A. FIG. 12 illustrates an example of a case where the frequency division ratio N1 of the frequency divider 52B is “4”, and the frequency division ratio of the frequency divider 52A is “16 (that is, “2×N×N1” in a case where N is 2)”. That is, in the example in FIG. 12, the frequency divider 52B divides the frequency of the feedback signal S4 into four frequencies, and thus the second drive signal S2 having a D/A conversion cycle t2 that is four times one cycle t1 in the feedback signal 54 is obtained. In addition, the frequency divider 52A divides the frequency of the feedback signal S4 into sixteen frequencies, and thus the first drive signal S1 in which a period t3 that is four times the D/A conversion cycle t2 is set as one cycle is obtained. According to the frequency dividers 52A and 52B configured as described above, the first drive signal S1 and the second drive signal S2 are generated so that the first signal element S1 _(i) and the second signal element S2 _(i) correspond to each other in a relationship of “1:N (here, two)”. In addition, the first drive signal S1 can be generated without waiting generation of the second drive signal S2, and thus it is possible to generate the first drive signal S1 and the second drive signal S2 in parallel.

In the MEMS mirror mechanism 3 illustrated in FIG. 2, FIG. 10 and FIG. 11, the first drive coil 34 for swinging the first movable unit 31 is provided in the first movable unit 31 and the second drive coil 35 for swinging the second movable unit 32 is provided in the second movable unit 32, but the MEMS mirror mechanism 3 may be configured as follows. As an MEMS mirror mechanism 3 of a first modification example, a drive coil for swinging the first movable unit 31 and a drive coil for swinging the second movable unit 32 may be provided in the second movable unit 32. Alternatively, as an MEMS mirror mechanism 3 of a second modification example, a single drive coil for swinging the first movable unit 31 and the second movable unit 32 may be provided in the second movable unit 32.

In the MEMS mirror mechanism 3 of the first modification example and the MEMS mirror mechanism 3 of the second modification example, the electromotive force monitoring coil may be provided in the first movable unit 31, and in this case, the electromotive force signal S3 corresponding to an electromotive force corresponding to swinging of the first movable unit 31 may be output to the control unit 5, 5A from the electromotive force monitoring coil. Alternatively, in the MEMS mirror mechanism 3 of the first modification example and the MEMS mirror mechanism 3 of the second modification example, the electromotive force monitoring coil may be provided in the second movable unit 32, and in this case, the electromotive force signal S3 corresponding to an electromotive force corresponding to swinging of the first movable unit 31 may be output to the control unit 5, 5A from the electromotive force monitoring coil. In the MEMS mirror mechanism 3 of the first modification example and the MEMS mirror mechanism 3 of the second modification example, since the second movable unit 32 is vibrated by the drive coil provided in the second movable unit 32, and the vibration is transmitted to the first movable unit 31 to swing the first movable unit 31, even in a case where the electromotive force monitoring coil is provided in the second movable unit 32, it is possible to measure an electromotive force corresponding to the swinging of the first movable unit 31. Alternatively, in the MEMS mirror mechanism 3 of the first modification example and the MEMS mirror mechanism 3 of the second modification example, the electromotive force signal S3 corresponding to an electromotive force generated in the drive coil (that is, the drive coil provided in the second movable unit 32) in correspondence with swinging of the first movable unit 31 may be output to the control unit 5, 5A from the drive coil.

In addition, the control unit 5, 5A may control the light source 2 so that the outgoing period T2 a corresponds to a first drawing period (a first lighting-on period: a period in which the control unit 5, 5A causes the light source 2 to emit the laser light L1), and the incoming period T2 b corresponds to a second drawing period (a second lighting-on period: a period in which the control unit 5, 5A causes the light source 2 to emit the laser light L1), and may repeat generation of the second signal element S2 _(i) in both the first drawing period and the second drawing period. According to this configuration, in the first drawing period and the second drawing period, it is possible to suppress occurrence of a deviation in the corresponding relationship between the first drive signal S1 and the second drive signal S2. Note that, in this case, an image of two frames is formed by m times of reciprocation (m: an integer of two or greater) of an irradiation region of the laser light L1 in the horizontal direction, and one time of reciprocation of the irradiation region of the laser light L1 in a vertical direction. In addition, the second drive signal S2 in this case, for example, is a triangular wave in which the outgoing period T2 a and the incoming period T2 b are mutually equal to each other.

In addition, the first drive signal S1 may be a sinusoidal wave or the like without limitation to the rectangular wave as long as the first drive signal S1 is an electric signal in which one swing of the mirror 3 a with respect to the first axial line A1 as a central line is set as one cycle T1. In addition, the second drive signal S2 may be a sinusoidal wave or the like without limitation to the triangular wave as long as the second drive signal S2 is an electric signal in which one swing of the mirror 3 a with respect to the second axial line A2 as a central line is set as one cycle T2. In addition, in the second signal element S2 ₁ of the second drive signal S2, the voltage value may not be constant, and may increase or decrease.

In addition, a circuit that modulates the frequency of the first drive signal S1 to conform to the resonance frequency of the mirror 3 a may be a DDS (direct digital synthesizer) circuit or the like without limitation to the PLL circuit 51.

The control unit 5, 5A may generate not only the first drive signal S1 in which a period varies from the first signal element S1 _(i) in which a period varies, but also the first drive signal S1 in which a period is constant from the first signal element S1 _(i) in which a period is constant. Even when the control unit 5, 5A generates the first drive signal S1 in which the period is constant from the first signal element S1 _(i) in which the period is constant, a period of the first drive signal S1 input to the MEMS mirror mechanism 3 may vary due to a variation of the resonance frequency of the mirror 3 a. Even in this case, according to the scanning device 1, the first drive signal S1 and the second drive signal S2 are generated so that m times of reciprocation of the irradiation region of the laser light L1 in the horizontal direction and one time of reciprocation of the irradiation region of the laser light L1 in the vertical direction correspond to each other.

In addition, the scanning device 1 may be used in various aspects such as a helmet-embedded type, an eyeglass type without limitation to the vehicle-mounted type. In addition, the scanning device of the present disclosure can be used in a distance image sensor. In the distance image sensor, a distance measurement region is scanned with laser light emitted from a scanning device, and laser light reflected from the distance measurement region is detected by a light detector. In the distance image sensor, a distance is measured with respect to respective sites in the distance measurement region that is scanned with the laser light on the basis of time until the laser light is detected with the light detector after the laser light is pulse-oscillated from a light source of the scanning device. A control unit of the scanning device which is used in the distance image sensor generates a first drive signal and a second drive signal so that m times of reciprocation (m: an integer of two or greater) of an irradiation region of the laser light in the first direction and one time of reciprocation of the irradiation region of the laser light in the second direction correspond to each other.

In addition, the process of making the first signal element S1 _(i) and the second signal element S2 _(i) correspond to each other (that is, the process of making a plurality (N pieces) of the second signal elements S2 _(i) correspond to the first signal element S1 _(i) in a ½ cycle period in the first drive signal S1) may not be repeated in a total period of the lighting-on period. That is, the above-described process may be repeated only in a partial period that is included in the lighting-on period and may not be repeated in a remaining period that is included in the lighting-on period. For example, in the remaining period, one piece of the second signal element S2 _(i) may correspond to one piece of the first signal element S1 _(i).

In addition, in the embodiment, a method of generating the second drive signal S2 by dividing the frequency of the signal (the feedback signal S4 or the first drive signal S1) based on the electromotive force signal S3 is illustrated, but the method of generating the second drive signal S2 is not limited to the above-described method. That is, the second drive signal S2 may be generated by a method other than the above-described frequency division. In a case where the second drive signal S2 is generated by a method other than the frequency division, a plurality (N pieces) of second signal elements corresponding to the first signal element S1 _(i) in ½ cycle (T½) of the first drive signal S1 may have periods having lengths different from each other.

FIG. 13 illustrates a case where N is two, a second signal element S2 a corresponding to the first half of the ½ cycle of the first drive signal S1 occupies ⅓ of ½ cycle of the first drive signal S1, and a second signal element S2 b corresponding to the second half occupies ⅔ of the ½ cycle of the first drive signal S1. In this example, the second drive signal S2 is constituted by only a signal element in a period that is an integral multiple of that of the second signal element having a minimum period. Specifically, the second drive signal S2 is constituted by a signal element (that is, the second signal element S2 a) in a period that is one time the period of the second signal element having a minimum period, and a signal element (that is, the second signal element S2 b) in a period that is two times the period of the second signal element. However, the second signal element may not have a period that is an integral multiple of the period of the second signal element having the minimum period. For example, in the example illustrated in FIG. 13, the period of the second signal element S2 b may not be an integral multiple of the period of the second signal element S2 a. As an example, the second signal element S2 a may occupy a period that is 0.48 times the ½ cycle of the first drive signal S1, and the second signal element S2 b may occupy a period that is 0.52 times the ½ cycle of the first drive signal S1. 

What is claimed is:
 1. A scanning device comprising: a light source configured to emit laser light; an MEMS mirror mechanism including a mirror configured to reflect the laser light emitted from the light source, the MEMS mirror mechanism being configured to reciprocate an irradiation region of the laser light in a first direction by swinging the mirror with respect to a first axial line as a central line, and reciprocate the irradiation region in a second direction that intersects the first direction by swinging the mirror with respect to a second axial line as a central line that intersects the first axial line; and a control unit configured to generate a first drive signal for swinging the mirror with respect to the first axial line as a central line and a second drive signal for swinging the mirror with respect to the second axial line as a central line, and input the first drive signal and the second drive signal to the MEMS mirror mechanism, wherein the first drive signal is an electric signal in which one swing of the mirror with respect to the first axial line as a central line is set as one cycle, the second drive signal is an electric signal in which one swing of the mirror with respect to the second axial line as a central line is set as one cycle, and in a lighting-on period in which the light source emits the laser light in the one swing of the mirror with respect to the second axial line as a central line, the control unit is configured to generate the first drive signal and the second drive signal by repeating a process of generating N pieces (N is an integer of two or greater) of second signal elements which respectively constitute the second drive signal to correspond to a first signal element in a ½ cycle period in the first drive signal.
 2. The scanning device according to claim 1, wherein the control unit is configured to repeat a process of generating N pieces of the second signal elements that respectively have a period that is 1/N times a period of the first signal element to correspond to the first signal element in the lighting-on period.
 3. The scanning device according to claim 1, wherein the first drive signal is an electric signal for resonating the mirror with respect to the first axial line as a central line, the second drive signal is an electric signal for linearly operating the mirror with respect to the second axial line as a central line, and the control unit modulates a frequency of the first drive signal to conform to a resonance frequency of the mirror.
 4. The scanning device according to claim 3, wherein the control unit is configured to generate the second drive signal by dividing a frequency of a feedback signal corresponding to a resonance frequency of the mirror in a frequency division ratio N1 (N1 is an integer of two or greater), and generate the first drive signal by further dividing a frequency of the second drive signal in a frequency division ratio 2×N.
 5. The scanning device according to claim 3, wherein the control unit is configured to generate the second drive signal by dividing a frequency of a feedback signal corresponding to a resonance frequency of the mirror in a frequency division ratio N1 (N1 is an integer of two or greater), and generate the first drive signal by dividing a frequency of the feedback signal in a frequency division ratio (2×N×N1).
 6. The scanning device according to claim 1, wherein the control unit is configured to control the light source so that in the one swing of the mirror an outgoing period corresponds to the lighting-on period, and an incoming period corresponds to a lighting-off period.
 7. The scanning device according to claim 1, wherein the control unit is configured to control the light source so that in the one swing of the mirror, an outgoing period corresponds to a first lighting-on period, and an incoming period corresponds to a second lighting-on period, and repeat generation of the second signal element in both the first lighting-on period and the second lighting-on period.
 8. The scanning device according to claim 1, wherein the control unit is configured to generate the second signal element to correspond to the first signal element in a current one cycle period in the first drive signal.
 9. The scanning device according to claim 1, wherein the control unit is configured to generate the second signal element to correspond to the first signal element in an immediately previous one cycle period in the first drive signal.
 10. The scanning device according to claim 1, wherein the MEMS mirror mechanism includes: a first movable unit provided with the mirror; a second movable unit configured to support the first movable unit to be swingable with respect to the first axial line as a central line; a support unit configured to support the second movable unit to be swingable with respect to the second axial line as a central line; a drive coil that is provided in the second movable unit; and a magnet configured to generate a magnetic field acting on the drive coil.
 11. The scanning device according to claim 1, wherein the light source is configured to emit the laser light for projection display, and the control unit is configured to generate the first drive signal and the second drive signal so that an image of one frame or two frames is formed by in (in is an integer of two or greater) times of reciprocation of the irradiation region in the first direction and one time of reciprocation of the irradiation region in the second direction when the m times of reciprocation of the irradiation region in the first direction and the one time of reciprocation of the irradiation region in the second direction correspond to each other.
 12. The scanning device according to claim 11, wherein the control unit is configured to control the light source so that the laser light is modulated in correspondence with a position of the irradiation region.
 13. The scanning device according to claim 11, wherein the control unit is configured to repeat generation of the second signal element while fluctuating a frame rate. 